unixon1995

<div class="box">
  <svg><line x1="0" y1="100%" x2="100%" y2="0" stroke-width="1" stroke="#fff"></line></svg>
</div>

.box {
  width: 100%;
  height: 500px;
  position: relative;
}

svg {
  width: 100%;
  position: absolute;
  height: 100%;
  left: 0;
}